A method for forming single crystal AlN thin films by a molecular beam epitaxy method, or the like, is known (for example, Japanese Patent Unexamined Publication Nos. H8(1996)-2999 and H9(1997)-309795).
However, since an AlN has a large band gap energy such as 6.5 eV, and an acceptor or a donor itself has a low impurity level of 500 meV (4000K), carriers cannot be activated at room temperature. As a result, only AlN thin films of high resistivity can be obtained.